Transformation of Schizosaccharomyces pombe with the previously cloned putative chitin synthetase 2 gene resulted in expression of the synthetase in S. pombe, thus showing that the cloned gene is indeed the structural gene for the enzyme. Disruption of the gene in Saccharomyces cerevisiae led to inability of the yeast cells to form a septum and divide. This result provided for the first time unequivocal evidence that chitin synthetase 2 is essential for the formation of septum chitin and that blocking of synthesis of a cell wall component results in death of a fungal cell. Chitin synthetase 1 is not required for septum formation. Under certain conditions, however, a chitinase that normally acts in cell separation may become exceptionally active, with a potential for damaging the cell wall and causing lysis. Recent results suggest that under those circumstances presence of chitin synthetase 1 leads to increased synthesis of chitin and prevents cell lysis, i.e. chitin synthetase 1 appears to function as an emergency or repair enzyme. The enzyme that catalyzes the biosynthesis of the major structural polysaccharide of the yeast cell wall, beta(1-3) glucan synthetase, was previously separated into two fractions, a soluble GTP-binding regulatory component and a membrane-bound, presumably catalytic, component. By using a combination of detergents, the catalytic fraction has been solubilized. Each component is now available in soluble form and free From the other one.